Evaluation of alternative dam operations on the movement and habitat use of bull trout and westslope cutthroat trout.

The goal of this project is to quantify the operational impacts of Hungry Horse Dam on native bull trout and westslope cutthroat trout in the upper Flathead River system, Montana. This instream flow study involves developing habitat suitability functions for native fishes, and then use a three-dimensional IFIM (Instream Flow Incremental Methodology) model to evaluate the impacts to critical habitat associated with hydropower and flood control operations at Hungry Horse Dam, located on the South Fork Flathead River. Suitability curves based on empirical telemetry data below the dam will be combined with two-dimensional hydraulic simulations of river hydraulic characteristics (i.e., stream bed elevations, mean column velocity, habitat type) in a GIS analysis format to determine habitat area as a function of stream flow. Estimations of usable habitat from the calibrated IFIM models will be used to rank the alternative operating strategies based on the amount of available habitat for each target species and lifecycle stage of salmonids in the Flathead River. Using the IFIM models, estimates of total usable area will be obtained for each species and life stage for three specific operational strategies: historic (pre-dam), water budget flow augmentation for migrating fish recovery, and the proposed Mainstem Amendments in the Columbia River Power and Flood Control System. Our preliminary results explain the importance of maintaining natural connections and a diversity of complex habitats over a large spatial scale to conserve the full expression of life history traits and processes influencing natural dispersal of bull trout populations. This research will provide managers with information to restore and enhance critical river corridor habitat through flow augmentation that maximizes critical feeding and rearing habitats for native salmonids in the system.